1. Field of the Invention
The present invention relates to kneading/extruding equipment and an operation control method thereof.
2. Description of the Related Art
As the kneading/extruding equipment, for example, a resin extruder as shown in Japanese Patent No. 3889941 is known.
The resin extruder described in the above-mentioned bulletin comprises: a raw material feeder; an extruding machine for extruding raw material from the raw material feeder while kneading and melting it; and serially-arranged first (first-stage) and second (latter-stage) gear pumps for discharging resin as a kneaded material extruded by the extruding machine.
An operation control device in this resin extruder comprises a first filtering device provided between the first-stage gear pump and the latter-stage gear pump, a second filtering device provided on the discharge side of the first-stage gear pump, a first feedback control means used in molding, and a second feedback control means used at start-up and in change of discharge rate.
The first feedback control means is configured to set the rotational speed of the latter-stage gear pump to a set speed and feedback-control the speeds of the raw material feeder, the extruding machine and the first-stage gear pump so that the pressure before the latter-stage gear pump becomes a set pressure.
The second feedback control means is configured to feedback-control the speeds of the first-stage and latter-stage gear pumps respectively so that the pressures before the gear pumps become set pressures and further to feedback-control, when the speed of the latter-stage gear pump reaches a set speed, the raw material feeder, the extruding machine and the first-stage gear pumps while keeping the speed of the latter-stage gear pump at this set speed.
However, the above-mentioned related art has the following problems.
1) Since the speeds of the raw material feeder and the extruding machine are changed during control, in the feedback control from the latter-stage gear pump, the kneaded or mixed state of resin in the extruding machine is greatly varied due to a slow response to a change of condition in the upstream, resulting in a prolonged time to a uniformed product quality (or, leading also to a material loss).
2) When the speeds of the raw material feeder and the extruding machine are feedback-controlled so that the resin pressure before the latter-stage gear pump becomes constant in steady operation (molding), the response rate of the resin pressure control to the change of condition in the upstream is reduced. As a result, the resin pressures before the first-stage and latter-stage gear pumps can exceed mechanical design pressures due to enhanced fluctuations of the resin pressures to damage devices before the first-stage and latter-stage gear pumps and the respective gear pumps.
3) When the switching from the control method in change of discharge rate to the control method in steady operation is performed at start-up, stable operation switching can not be performed since the whole control system becomes unstable to enhance the fluctuations of the resin pressures before the respective gear pumps.
4) When the resin extruder is increased in size to respond to an increase in production rate, the above-mentioned problems of 1) and 3) become more significant since it takes time to accelerate/decelerate this resin extruder and the pressure before the latter-stage gear pump increasingly becomes unstable.